In the course of treating and preparing subterranean wells for production, a downhole packer may be run into the well on a work string or a production tubing. Packers are suspended in the wellbore, or in a casing in the wellbore, from a tubing string, or the like, and are activated, or set, so that one or more packer elements engage the inner surface of the wellbore or casing. The purpose of the packer is to support production tubing and other completion equipment, and to seal the annulus between the outside of the production tubing and the inside of the well casing to block movement of fluids through the annulus past the packer location.
Packer setting methods may be classified as mechanical, hydraulic, or electric. Hydraulic methods include both hydraulically setting with surface pressure or hydrostatically setting with well pressure. Hydraulically setting a packer may refer to applying fluid pressure to the tubing, which then may be translated to a plugging device below the packer. Hydrostatically setting a packer may refer to relying on the downhole well pressure for setting and applying tubing and/or casing pressure on the packer to release hydrostatic pressure.
The process of perforating and fracturing is a well-known method of increasing production of a well. Packers may be used to isolate a designated zone of a wellbore before perforating or fracturing the well. The process of fracturing the well generally produces debris within the wellbore. Some of this debris may be removed from the wellbore by reverse circulation of the well fluids. However, reverse circulation cannot remove all debris from the wellbore, and some well configuration may increase the difficulty in removing the debris via reverse circulation. Thus, it may be desirable to provide a tool adapted to collect debris below the packer so that the debris does not interfere with the other downhole operations. Expendable plug mechanisms may be used as a temporary barrier between perforations and the surface, or as a temporary bridge plug in the setting of a hydraulic packer. Some prior art expendable plugs rely on pressure differentials above and below the plug to expend the plug. Prior art plug mechanisms may include, but are not limited to, pump out plugs, expendable plugs, and pump-thru plugs. A pump-out plug and pump-thru plug may be expended by dropping a ball from the surface and applying pressure above the ball when it is on the seat of the plug. When the pressure from above exceeds the shear rating of shear pins holding the plug in place, the internal plug shears out. An expendable plug may be expended when a piston in the plug is mechanical shifted downward thereby unsupporting lugs used to latch the plug onto the packer.
One problem associated with such prior art expendable plugs is that debris within the wellbore may inhibit the function of the expendable plug mechanisms. Thus, as stated above, it may be desirable to provide a tool adapted to collect debris below the packer so that the debris does not interfere with the other downhole operations. Another problem associated with such prior art plugs is that the shear pin rating required to expend the plug mechanism may result in hydrostatic pressures that may exceed the pressure rating of other equipment used in the completion. Thus, it may be desirable to provide a locking mechanism for attaching the plug to the packer that may be disengaged or unlocked upon interaction with a downhole tool. Another problem associated with such prior art expendable plug mechanisms is the possibility of the plug expending prematurely. Thus, it may also be desirable to adapt a plug mechanism to be releasably engaged and only disengaged upon interaction with the downhole tool.